A World to Explore

Impressive, isn’t it? You can practically smell it steaming on your screen. Hard to believe this object is Miocene in age, about 6 million years old.Here’s another similar specimen in a top view, if we can say that.And here’s a side view. Notice the rich color, long, parallel striations, and “pinched” ends. If these aren’t fossil feces, officially known as coprolites, they’re excellent imitations. They’ve been prime attractions in our first paleontology lab.

These evocative objects are primarily made of siderite, making them dark and heavy. Our specimens above come from the Wilkes Formation (upper Miocene) in southwestern Washington state. They are enormously abundant and thus common in rock shops and museums around the world. In that is your first clue: how can feces with such exquisite detail be preserved so perfectly in such enormous numbers in so few places? My answer, along with many other geologists, is that these are pseudocoprolites made by inorganic means. Their extrusive nature and appropriate color gives us the illusion of poop.

I’m highlighting these objects this week because a paper appeared last month in the journal Lethaia making a case that they actually are biological in origin. Broughton (2016), in a long bit of prose and analysis, concludes that the Wilkes Formation objects are a mix of giant earthworm “mineralized intestinal remains (Type 2)” and coprolites “from unknown vertebrates” (Type 1). I don’t buy Broughton’s interpretations, but found them fascinating enough to make his paper part of a reading exercise in my paleontology class this month. The most relevant references are below so you can do your own reading and decide what these curious extrusions (or intestinal casts) are.

Let’s start with this excellent 2014 article by Brian Switek for National Geographic: “Was Six-Million-Year-Old Turd Auctioned for $10,000 a Faux Poo?” Yes, one of these curiosities actually sold for $10,370 at an auction … and it is over 100 centimeters long! (Check out the images in this NPR article on the auction. That would be an epic poop for anyone.) This auctioned specimen is an example of what Broughton (2016) calls Type 2; he believes they are essentially mineralized guts of really large burrowing earthworms. He makes his case by interpreting the striations as muscle fiber impressions, and the shapes as resulting from peristaltic motions inside the worms. (Seilacher et al., 2001, had similar ideas.) The smaller “faecal-like specimens”, like we have at Wooster, are his “Type 1”. As far as I can tell, only length separates Type 1 from Type 2 in Broughton’s classification and, as might be expected, “Some fragmentary Type 2 specimens may be misidentified as Type 1.” It is odd that Types 1 and 2 are identical in every feature but size, yet are given very different origin stories.

Critical observations to keep in mind as you explore this mystery: (1) These siderite objects have no inclusions of organic material — not a seed, woody bit, or bone fragment; (2) There are no associated vertebrate skeletal remains or other traces, and no evidence for earthworms either; (3) They are incredibly abundant in limited horizons, and unknown elsewhere; (4) They range in size from a centimeter or less to over 100 centimeters long; (5) You’d think you’d find a few squashed, now and then, or burrowed by insects, but they are in spectacular three-dimensional preservation.

I support the earlier interpretations of these excrement-appearing rocks as deformations of soft, plastic sediments by inorganic processes, as thoroughly developed by Spencer (1993), Mustoe (2001) and Yancey et al. (2013). They may have been extruded through rotting hollow logs by compaction, liquified by seismic activity, or squirted through cracks by natural gas emissions (which would be ironic!). That these pseudocoprolites were squeezed through something seems obvious; it is unlikely they came to us by way of animals.

Last month we featured a fossil slab kindly donated by Dale Chadwick of Lancaster, Pennsylvania. Dale is an enthusiastic fossil collector with a very useful website for his favorite sites and specimens. I promised to show the other side of this rock, and here it is.

Again, this is a fine sandstone from the famous Calvert Formation (lower to middle Miocene) exposed at the Calvert Cliffs, Plum Point, Calvert County, Maryland, in the stratigraphic Shattuck Zone 10. Some horizons are especially fossiliferous with large numbers of gastropods and bivalves. This is what we refer to us a death assemblage, meaning these shells are not preserved in their life positions but how they accumulated just before final burial. These rocks and their fossils were the initial basis of Susan Kidwell’s important work on taphonomic feedback, or how shell accumulations affect the succeeding living communities.

So what are the prominent fossils in this slab? Dale has the answers on his website. I’ve annotated the image and made a list below:

Earlier this month a gentleman stopped by The Department of Geology and donated the above beautiful slab of fossils to our program. Dale Chadwick of Lancaster, Pennsylvania, is an avid amateur fossil collector with a very useful website and considerable generosity. His gift to the department makes an excellent Fossils of the Week entry. Later I’ll show you the equally-impressive other side of this specimen!

We have here a fine sandstone from the famous Calvert Formation (lower to middle Miocene) exposed at the Calvert Cliffs, Plum Point, Calvert County, Maryland, in the stratigraphic Shattuck Zone 10. As you can see, some horizons are densely fossiliferous with large numbers of gastropods and bivalves. This is what we refer to us a death assemblage, meaning these shells are not preserved in their life positions but how they accumulated just before final burial. These rocks and their fossils were the initial basis of Susan Kidwell’s important work on taphonomic feedback, or how shell accumulations affect the succeeding living communities.

So what are the prominent fossils in this slab? Dale has the answers on his website. I’ve annotated the image and made a list below:

So how did several of these animals die on that seafloor long ago? You’ve probably guessed predation by looking at that round hole in specimen B, a lucinid bivalve.

The beveled nature of this round drillhole tells us it was made by a predatory naticid gastropod, which used its radula (a tongue-like device with sharp teeth) to penetrate the calcareous shell and damage the muscles holding it tight against the attack. About half the specimens in this slab show similar predatory penetrations. Wooster alumna Tricia Kelley did critical work on predation styles, intensities and evolutionary patterns with Calvert specimens like these.

MITZPE RAMON, ISRAEL — As part of our Shabbat trip today, Yoav Avni wanted to take me up Ada Canyon (N30.32973°, E34.91417°) to explore the Hazeva (Miocene) and Arava (Pleistocene). He cryptically said, “There will be places we can barely get through”. True, that. Above is Yoav at the start of the hike. Turns out this is a slot canyon with challenges.

“The narrow part begins”, he says helpfully.

At this point I have to take off my pack to reduce my sideways width.

And sideways with a twist is the only way through as the walls close in. Pro tip: Never do this when it is raining.

Now it gets problematic with boulder scrambling and claustrophobia.

A ladder! I never did mention my aching shoulder.

Steps cut in the rock and then a second ladder. Going down is always easier than going up, right?

A knotted rope to climb the cliff! Note the shadow of successful me at the top of the last obstacle. Wondering, though, what these climbs are like on the way back.

The view at the top of the mountain, though, really was spectacular. This is a view towards Be’er Ada, with the fault described in the previous post running diagonally across the background.

And yes, the geology along the way! It was very impressive. The Hazeva Formation is mostly sandstone with some layers of sandy conglomerate as in the above image. It was deposited in a wetlands with occasional floods (which produced the coarse layers). The cobbles are rounded cherts derived from Jordan to the east.

The Arava Formation was deposited in a desert much like what we see today. It is interbedded gravels (from wadis) and unconsolidated silts (from playas and saline lakes). Classic sed/strat material. It was all well worth the adventure for this aging geologist!

MITZPE RAMON, ISRAEL — Yoav Avni and I have a tradition on Shabbat. We drive somewhere to explore interesting geology and history unconnected to current projects. It’s not really work — it’s geotourism. We are, though, always talking about new ideas. Today we traveled south of Mitzpe Ramon into the “deep desert” of the Arava below the Negev Highlands.

The morning view south across Makhtesh Ramon was spectacular. It isn’t conveyed very well through an image only 585 pixels wide, but it is a perspective of unusual clarity. The purple streak at the top represents mountains in western Jordan. The haze just below them is in the Arava Valley. We are looking across most of the Negev.

Our mission today was to visit Be’er Ada (Bir Abu ‘Auda), an historic well, and the geology around it. (N30.32229°, E34.90701°, if you’re following at home.) The top image on this post is a view from the road to the well. Just above is a grove of acacia trees near the well. The abundance of these trees, and their good health, is an indication of accessible water.

Here is Yoav peering down into Be’er Ada. (“Be’er” means well.) It is at least twenty meters deep. The base is filled with silt, so it will have to be dug out to supply water again. This well is thousands of years old and has been a critical watering spot in the Negev for traveling groups. The next nearest well is to the east about 40 km away. Another 40 km or so to the west is another well. Be’er Ada was active as late as the 1950s, and likely had sporadic use afterwards. The water here accumulates on the impermeable clays of the Taqiya Formation (Paleocene).

This is a view from near Be’er Ada to the main geological interest for me: the the orangish Hazeva Formation (Miocene) topped unconformably by the gray Pleistocene Arava Formation. We will spend much more intimate time with these units in the next post. Note the graceful acacia trees.

This area is next to a complex fault system. On the left is a down-dropped block of Hazeva and Arava, with Cretaceous rocks on the right. The fault is also part of the reason for the subterranean water resources at Be’er Ada.

In the middle of the image is an example of the pareidolia so common in stark landscapes. Some people see a face in profile. Apparently tour guides like to call this the head of “Ada” for whom the well was named. However, there never was such a woman!

Note the excellent weather in these images. A perfect Negev day! Thank you to Yoav for being such a generous host.

This week we have a rather unimposing limestone cobble, at least from the outside. It was collected way back in 1989 by my student Genga Thavi (“Devi”) Nadaraju (’90) as part of a Keck Geology Consortium field project in southeastern Spain. It comes from the Los Banós Formation (Upper Miocene) exposed near the town of Abanilla. The holes are borings excavated into the carbonate matrix by marine animals. This cobble was tossed about in a coral reef complex that was part of the ancient Fortuna Basin.Seeing the cobble in cross-section makes it much more interesting. (Geologists love their rock saws!) We now see two categories of borings: one is large and flask-shaped, and the other a small network of spherical cavities. The large borings were produced by bivalves that tunneled into the limestone to make living chambers (domichnia) from which they could filter-feed. As the bivalve grew, the hole became deeper and wider. There was no escape — making and living in a boring like this is a lifetime occupation. These bivalve borings are classified as the trace fossil Gastrochaenolites lapidicus Kelly and Bromley, 1984. The smaller borings were made by clionaid demosponges that used acid to create a series of connected chambers, also for filter-feeding. These sponges could only penetrate about ten mm or so before their filtering became ineffective, so they are confined to the outer periphery of the cobble. The sponge borings are given the trace fossil ichnogenus Entobia Bronn, 1837.

On the inside surface of the largest boring (right side), encrusting tubes of a serpulid worm are just visible. This serpulid was also a filter-feeder. It took advantage of the cozy hole after the bivalve borer died and decayed. It is called a coelobite, or cavity-dweller. Serpulids would have had a rough time cementing to the outside of the cobble as it rolled around in this high-energy environment.

These two beautiful barnacles are from the Calvert Formation (Middle Miocene) exposed near Parker Creek in Maryland. They are likely of the genus Chesaconcavus. Barnacles are most unlikely crustacean arthropods, cousins of shrimp, crabs and lobsters. Most, like these above, cement themselves head-downwards on a hard substrate like a rock or shell (or boat hull), build a carapace around themselves of calcitic plates, and then filter-feed by kicking their filamentous legs in the water above to catch suspended food. They are entirely marine and usually live in shallow water.This is a top view of the barnacle pair. We can look straight into the carapace because the opercular plates, which form a kind of door system, have been removed. For barnacles, these are a healthy large size.Now we’ve turned the barnacles upside-down to see their attachment surface. The substrate to which they were glued is gone, so we can see the details of the basal plates. The barnacles may have just sloughed off a shell or rock, or maybe they were attached to an aragonitic shell that dissolved away. What is cool here is that we can see other organisms that were on the substrate the barnacles encrusted, including two smaller barnacles completely absorbed within the larger skeletons. This is again an example of bioimmuration. The smaller barnacles look like upside-down cones in this perspective. Note that in the apex of each you can see preserved opercular plates — the insides of the “doors” that are opened for feeding. In the fine-grained skeleton of the larger attachment surface you can see growth lines made by the large barnacles as they occupied the substrate. There are even some small serpentine impressions that may represent soft-bodied organisms that were bioimmured.Here’s a closer view of the above basal features. I love the frilly edge of the bioimmured barnacle in the top left.

This fossil has been sitting in a glass case outside my office door for nearly three decades. Only this year — in the desire to find more Fossils of the Week — did I bother to open the cabinet and take it out for a looksie. On the reverse was a 19th century label: “Titanotherium proutii, Badlands, SD”. That started me on a complicated journey through the literature to see just what sort of creature bore these magnificent molars, as well as the history of its discovery.In this occlusal (meaning the biting surface) view you can see in the beautiful flowing lines of the hard (dark) and softer (light) enamel that there are some serious cracks repaired with a dodgy yellowish glue. The specimen is very fragile — that glue has probably been holding it together for well over a century. These are classic plant-eating teeth for both cutting and grinding leaves, roots and small branches.The animal represented here is a titanothere, a large extinct mammal common in what would become the Badlands of South Dakota during the Paleogene. Above is a recreation of a relative of our species: Megacerops (Titanotherium) robustum. (The artist who drew this illustration in 1912 was Robert Bruce Horsfall, 1869-1948.) The titanotheres, now better known as brontotheres, were roughly the size and shape of rhinoceroses, but were actually more closely related to horses. They had elephant-like feet, inwardly-curved skull caps, and impressive horns on the nose.

I usually delight in tracking down taxonomic histories (the technical history of scientific names), but Titanotherium proutii has defeated me. The history of this taxon is convoluted beyond recovery — a sad tale of mistakes, misplaced fossils, specimens given multiple names, and over-zealous “splitting” of taxa. In other words, typical middle 19th century vertebrate paleontology. Mader (1998) says that Titanotherium Leidy 1853 (or 1852?) is a nomen dubium or “doubtful name”. Even the species, which later became Palaeotherium proutii, is nomen dubium. The names are simply worthless to science. I have been unable to figure out what the accepted name for our fossil now is.Joseph Leidy (1823-1891) named Titanotherium and (maybe) T. proutii (there is dispute as to who named it first). Leidy was a well known American biologist and paleontologist who taught first at the University of Pennsylvania and then Swarthmore College. He described and named the first nearly-complete dinosaur skeleton, Hadrosaurus foulkii. (It was found in the Cretaceous of New Jersey and he named it in 1858.) Leidy was also an early supporter of Charles Darwin and his the new theory of evolution, early enough for this to be an unpopular position. Edward Drinker Cope was one of his students, which forever places him at the beginning of the famous “Bone Wars” between Cope and Othniel Charles Marsh, which raged from 1877 to 1892. That epic conflict actually began in the New Jersey marl pits where Leidy’s hadrosaur was found. Leidy thus leaves us with a mixed legacy of discoveries, innovations and insights mixed with errors and folly. Just the sort of character we would expect on the frontier of a new science in a new country.Leidy’s 1853 (Plate XVI) figure of a jaw fragment of “Titanotherium proutii“.

References:

Leidy, J. 1853. The ancient fauna of Nebraska: or, a description of remains of extinct Mammalia and Chelonia, from the Mauvaises Terres of Nebraska. Smithsonian contributions to knowledge, vol. 6. Washington, Smithsonian Institution.

I long thought of this beautiful specimen as more rock than fossil. It is a scleractinian coral that has had its outer skeleton replaced by the silicate material agate and its interior skeleton completely hollowed out. The result is a geode that happens to also be a fossil.Then during last month’s North American Paleontological Convention in Gainesville, Florida, I saw the above specimens on display in the Florida Museum of Natural History. These fossils were so striking that I decided to highlight our single example.This is a view of the top surface of the Wooster specimen. In the upper left is an array of holes with crystals radiating away from them. These are remnants of the original corallites, and there is just enough information there for us to conclude the likely genus is Montastraea. This piece thus becomes an example of Florida’s official state stone. Here’s the official definition: “… a chalcedony pseudomorph after coral, appearing as limestone geodes lined with botryoidal agate or quartz crystals and drusy quartz fingers, indigenous to Florida.” Our specimen came from the Hawthorn Group of rocks near Tampa, Florida.The outside of the fossil shows horizontal banding remaining from the original growth lines in the coral, which is another clue that this is Montastraea. The coral made its skeleton of aragonite around 30 million years ago. After death and burial, silica-rich groundwater began to replace the aragonite on the surface of the coral with what later became banded agate. The interior dissolved away into a hollow cavity.

The common name for this fossil is “agatized coral“, and it is a collector’s item. It is apparently Florida’s only native gemstone. Pretty cool that their state rock and gemstone is a fossil!

References:

Scott, T.M. 1990. The lithostratigraphy of the Hawthorn Group of peninsular Florida. World Phosphate Deposits 3: 325-336.

These large brachiopods are of the species Terebratula maugerii Boni, 1933. They were found in Upper Miocene (Tortonian-Messinian) beds near Cordoba, Spain. Wooster acquired them through a generous exchange of brachiopods with Mr. Clive Champion in England.

The specimen on the left is oriented with the dorsal valve upwards. The ventral valve is below and visible at the top of the image. The ventral valve of terebratulids has a rounded opening through which the attaching device, called the pedicle, extended. The specimen on the right is shown with its ventral valve upwards. Since this is the largest valve, you can’t see the dorsal valve below.

I like these specimens because they have that beautiful fold in the center of the shell. This is much more pronounced than in the usual terebratulid brachiopod (it is said to be “strongly plicated“), so students get to see some variety in this large but generally uniform group.

By the Cenozoic, brachiopods are rather rare in fossiliferous deposits. Shelly beds from the Paleocene on are dominated by mollusks, especially bivalves. This large brachiopod, though, is an exception found in the Upper Miocene shellbeds of southern Spain. It is found in meter-thick accumulations, making it for a very short time a significant carbonate component in marine sediments. Terebratula maugerii was most common in the deep subtidal in high-energy deposits. (See Reolid et al., 2012, for details.)Finally, brachiopods are commonly called “lamp shells“, which makes no sense to most modern students. They were given this nickname way back in the 18th century because of their resemblance to Roman oil lamps, such as those figured above in the same orientation as our shells. These were filled with oil through the central hole and a wick was placed in what we now see as the “pedicle opening”. It is an archaic comparison, but it works!